Plasticizing method



March 21, 1939.

s. E PALMER PLASTICIZING METHOD Filed March 23 INVENTOIL SjvencerEPalmer .l g m-bed ATT Patented M81321, 1939 2,150,939

UNITED STATES PATENT OFFICE Application March 23, 1936, Serial No. 70,201 4 Claims. (01. 106-40) This invention accordingly has as its princi- While this technique is well adapted for use with pal object, to provide a method of employing the a. number of the well-known cellulose derivative solvent plasticizers in the plasticizing of cellulose or above ordinary temperatures upon the parand cellulose acetate propionate. Another ob- 2 26 having the property or ability of forming solid a uniformly plasticized cellulose organic acid ester solutions or gels with the ester, have a pronounced plastic in which the plasticizer is homogeneously and unavoidable tendency to become locally abdistributed. Other objects will appear hereinsorbed on the ester particles or masses with after.

which they come in contact, regardless of whether These objects are accomplished by the follow- 30 the material is ground or unground and no ing invention which, in its broader aspects, com- 30 85 cellulose organic acid ester and solvent plastivent action upon the material. As indicated 40 that this is not the case and that even this drasfive Diametrically opposed to this idea, and 40 plastics in accordance with vthe best accepted plasticizer in the cellulose organic acid ester ma- It has been proposed t jncgrporate .tm typ melting point of the plasticizer, since as a pracpla'gfigizer thrgugh th medium of tu tical matter, the plasticizer should be in liquid solventtor the plasticizer and the cellulose or- 7 or at least semi-liquid state under the conditions fled. Upon removal of ticizer is subjected to of in order to facilitate proper-mechanical working.

In'the following examples and descriptio' I have set forth several of the preferred embodiments of my invention, but it is to be undertood that they are included merely for purposes of illustration and not as a limitation thereof.

The method of the invention may be conveniently carried out in any simple type of apparatus provided with means for cooling the mix to the desired temperature and with means for mechanically agitating the material sufiicientiy to bring the plasticizer into intimate contact with the cellulose derivative material. A conventional form ofsuch a device is illustrated in the single time of the accompanying drawing. 4

A mixing device may, for example, comprise a mixing vessel I suitably mounted upon a base 2 and having double walls 3 and l providing a water Jacket I for the circulation of cold water or other refrigerating or cooling fluid. The Jacket I is supplied with the cooling fluid by means of inlet conduit 6, while outlet conduit 1 conveys the cooling fluid therefrom. The numerals 8 and 0 designate mechanical mixing derotatable shafts i0 and II, respe tiv source of power (not shown) and provided with blades l2 and If respectively for cutting through the mass undergoing mixing'and of so manipulating it that all of the cellulose derivative material are, intimately brought in contact with the plasticizer. A cover it is conveniently provided in order that the temperature of the device may be more eflectively controlled and-in order that the operation may be carried out with no loss or contamination of material.

Example I.-l00 parts by weight of cellulose acetate ground to a particle size corresponding to approximately 80 mesh are placed in an apparatus of the type of that shown in the single figu e of the weight of dimethyl phthalate, the plasticizer being introduced at a temperature of about 15 C., the temperature of the mix being maintained at about 15 C. by circulating through the water Jacket of the device a stream of water cooled to or below this temperature. The mixture of cellulose acetate and plasticizer is then subjected to mechanical mixing for a period of minutes by turn it over and expose new surfaces for contact with the plasticizer. This operation is carried out at constant temperature as previously speciit is found that mixing chamber. the plasticizer plasticized mass, which is in the form of a damp powder in which the particles are nevertheless not appreciably agglomerated, may then be cally if desired. for the purpose or it may be employed directly without such treatment, in a moldoperation.

Ezcmple II.-100 parts by Wei t of cellulose acetate propionate ground'to a particle size corresponding to about 80-100 mesh are mixed as in I Example I with parts by weight of dimethyl thalate. The initial temperature of the pissticizer is 10 C. and the mixing vessel is maintained at approximately the same temperature while the celluloseacetate propionate and plasmechanical mixing for a the mixture from theareas period of so minutes. After permitting the material to come to atmospheric temperature, it is found that the plasticizer has been homogeneously and uniformly incorporated with the cellulose acetate propionate particles, resulting in the production of a composition which may then be directly employed in a molding operation or may be otherwise worked as desired.

Example 1Il.-100 parts by weight of cellulose propionate of 47% propionyl content ground to a particle size corresponding to 80 mesh are placed together with parts by weight of dibutyl temperaabout mechanical mixing for a period of 30 minutes. It is found that the resulting mixture is a uniformly and homogeneously plasticized composition of cellulose propionate suitable for use in a molding operation and for other uses.

Example IV .-100 parts by weight of cellulose butyrate of 52% butyryl ground to a particle size of 80 mesh are mixed as in the preceding examples with 30 parts by weight of benzyl benzoate, the initial temperature of the plasticizer being about 10 C.'for a period of 30 minutes. The product is a uniformly and homogeneously plasticized molding composition.

While I have in the above examples chosen to illustrate my invention by reference to the plasticizing of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, my inventionis also applicable to the plasticizing of other cellulose organic acid esters. It is applicable to either the fully esterifled or hydrobut particularly to the hydrolyzed esters as these are particularly adapted for molding compositions due to their inherently greater plasticity than the unhydrolyzed esters.

Likewise, while I have chosen to illustrate my invention by reference to theuse of certain speciflc plasticizers, such as dimethyl phthalate, my invention includes the use of any of thoseplasticizers which, at ordinary atmospheric temperatures, have a pronounced solvent action upon the I ployed cellulose organic acid esters, is about 15 C.'

A table is given below listing some of the best solvent plasticizers for a typical cellulose organic acid ester, namely, cellulose acetate, and showing the approximate critical temperature for each plasticizer, that is, the temperature at which the plasticizer becomes actively solvent toward the ester:

Critical.

Plasticizer mm Ethylene l col dipropionate Glyceryl c oro dipropionate..

GmQo-m" evident that I may employ material of varying degrees of fineness. I may, for example, employ material which has been ground until it will pass a 40-300 mesh screen. This material, of course,

a condition in which it may be used in a molding operation. As

or injection moldin What I claim is: 1. The method of uniformly and homogeneting point of dimethyl phthalate and about 15 C. and thereafter raising the temperature of the mixture to a point at'whlch the dimethyl phthalate becomes an active solvent of the ester.

at which the dimethyl phthalate becomes an active solvent of the cellulose acetate.

SPENCER E. P LMER. 

